Hot Deserts

Desert - an area that receives less than 250mm of rainfall per year.

Where are hot deserts found?

• Mostly found in dry continental areas.
• Away from coasts.
• In a belt approximately 30 degrees North and South. 

Climate:

• At these latitudes air that has risen at the Equator descends forming a persistent belt of high pressure.
• Lack of cloud and rain.
• Very high daytime temperatures.
• With the lack of cloud cover, temperatures can be below freezing at night during the winter.

Soil:

• Usually shallow with a coarse, gravelly texture.
• Hardly any leaf fall so the soil isn't very fertile.
• Lack of rainfall and plant material mean the soil is often dry. 

• People living in the desert grow a few crops where there are natural springs or well to water, usually in the desert fringes.
• Indigenous people are often nomadic - they travel all the time in search of food and water for their herds, which are mostly goats and sheep.

The biotic components of hot deserts and the abiotic components are closely related - if one of them changes, the others are affected.

• Plans gain their nutrients from the soil, and provide nutrients and water to the animals that eat them. In turn, animals spared seeds through their dung, helping plants to reproduce.
• The hot and dry climate affect the soil in deserts. Soils are salty due to high evaporation and relatively low in nutrients because there is little decomposition of dead plant material by fungi and bacteria. This means that plants struggle to grow.
• The sparse vegetation limits the amount of food available, so the desert can only support low-density populations of animals.
• Water supplies in deserts can be extremely scarce - rainfall is very low and the coarse desert soil means that any rain that does fall quickly drains away. Animals and people have to find ways of coping, e.g, by constantly moving to new places or digging deep wells.

• People have to irrigate (artificially water) the land in order to be able to grow crops. Drawing unsustainable amounts of water from wells lowers the level of water underground - reducing the amount available to other plants. Some plant species and the animals that depend on them can struggle to survive as a result.
• Changes to components of the ecosystem, such as allowing cattle to overgraze vegetation, can have knock-on effects on the whole ecosystem, e.g, by causing soil erosion. Without plant roots to stabilise the soil, wind can blow sand particles away. Soil erosion can lead to clouds of dust in the atmosphere which can change the climate of deserts - reducing rainfall and making them even drier.

• Hot deserts have relatively low biodiversity. 
• Small areas around ephermal (temporary) ponds or rivers or along the desert margins have the highest levels of biodiversity and contain a high proportion of species that are endemic (unique) to the desert.
• Areas with water also have the highest density of human populations. Human development threatens biodiversity by increasing desertification and by over-using or contaminating water supplies.
• Development around the desert margins also means that habitats are being divided up by roads - threatens animals that migrate over large distances to find food and water.
• Global warming is generally making deserts hotter and drier, forcing some species to move to cooler areas to cope with the rising temperatures. 
• Species that are already at the limits of their environment don't have anywhere else to go - risk of decline or extinction. 
• Low biodiversity and pressure from development and climate change mean that deserts contain many biodiversity hotspots - places where there are a high proportion of endemic species that are threatened with extinction.

• Plant roots are extremely long or reach very deep water supplies or spread out very wide near the surface to catch as much water as possible when it rains.
• Many plants, e,g, cacti, are succulents. They have large, fleshy stems for storing water and thick waxy skin to reduce water loss (water loss from plants in called transpiration.)
• Some also have sharp spines and toxins to stop animals stealing water from their stems.
• Some plants have small leaves or spines - gives them a low surface area, reducing transpiration.
• The seeds of some plants only germinate when it rains - the plants grow, flower and release seeds in just a few weeks, which makes sure they only grow when there's enough water to survive.

Animal adaptations:

• Some animals are nocturnal to stay cool in burrows during the day or sit still in the shade whilst it's hottest, e.g, fennec foxes.
• Desert animals also often have long limbs or ears, providing a large surface area to lose heat from. 
• Lizards and snakes are able to tolerate high body temperatures.
• Some bigger animals store large amounts of fat which they break down into water when needed, e.g, camel.
• Some animals get all the water they need from the food they eat.
• Adaptations to cope with sand - triple eyelids, long eyelashes, closing nostrils, flat feet. 

• Thick waxy skin - to store lots of water.
• Spikes - protection and minimise surface area to reduce water by transpiration. 
• Large fleshy skin.
• Shallow widespread roots to get underground water.
• Large surface area from round shape.
• Fibrous roots - spread out wide from plant, grow close to the ground's surface and collect surface water.
• Taproots - anchor the cactus and reach deep water supply.

Camel adaptations:

• Store fat in humps - provides energy at times of food shortage.
• The ability to go for a long time without water - they lose little through urination and sweating. 
• The ability to tolerate high temperatures.
• Large, flat feet - to spread their weight.
• Thick skin on knees - protection when they kneel.
• Two rows of long eyelashes - protects eyes from sand and sun. 
• Leathery mouth - chewing thorny plants.
• Slit-like nostrils - able to open and close to prevent from sand. 

• One of the major hot deserts of the world.
• Stretches across north-west India and into Pakistan. 
• It is the most densely populated desert in the world.

The desert environment -

• Mainly sandy hills with extensive mobile sand dunes and clumpsnn of thorn forest vegetation. 
• Low rainfall.
• Sandy soils and not very fertile.
• They drain very quickly so there is little surface water. 

1. Mineral extraction

• The desert region has valuable reserves of minerals which are used all over India and exported across the world. 
• Important minerals: gypsum, feldspar, phospherite, kaolin. 
• Valuable reserves of stone in the region. 
• Used domestically and for export. 

2. Tourism

• Has become a popular tourist destination in recent years.
• Desert safaris on camels have become popular. 
• Beautiful landscapes. 

3. Energy

• The Thar Desert is a rich energy source.
• Coal - extensive coal deposits in parts of the desert and a thermal energy plant has been constructed.
• Oil - large oilfield  which could transform the local economy. 
• Wind - wind park is India's largest wind farm.
• Solar - Thar Desert has ideal conditions for solar power. 

4. Farming

• Most of the people living in the desert are involved in subsistence farming. 
• They survive in the hot and dry conditions by grazing animals on the grassy areas and cultivating vegetables and fruit trees. 
• Commerical farming has been made possible by irrigation.
• The construction of the Indira Ghandi Canal has revolutionised farming and crops such as wheat and cotton. 
• Other crops grown under irrigation are pulses, sesame, maize and mustard.

The Thar Desert suffers from extremely high temperatures. This presents challenges for people, animals and plants living in this environment:

• Working outside in the heat if the day can be very hard, especially for farmers.
• High rates of evaporation lead to water shortages which affect people as well as plants and animals. 
• Plants and animals have to adapt to survive in the extreme heat. 

Water shortages

• Water supply has become a serious issues in the Thar Desert.
• As the population has grown and farming and industry have developed, demand for water has increased.
• Water in this region is a scarce resource.

Water sources:

• Traditionally, drinking water for people and animals is stored in ponds which are natural and manmade. 
• There are a few rivers and streams that flow through the desert but only flow after rainfall - most settlements are found along these rivers
• Some water can be found at underground surfaces using wells but this water is salty and not very good quality.

The main form of irrigation in the desert is the Indira Gandhi Canal.

This source of fresh water has transformed an extensive area of the desert and has revolutioned farming.

• Commerical farming, growing crops such as wheat and cotton, now flourishes in an area that used to be scrub desert.
• Two of the main areas to benefit from the canal are centered on the cities of Jodhpur and Jaisalmer where a majority of the land is under irrigation.
• The canal provides drinking water to many people in the desert. 
• Constructed in 1958, the canal has a total length of 650km.

• Due to the very extreme weather and presence of vast barren areas, there is a very limited road network across the Thar Desert. 
• The high temperatures can cause the tarmac to melt and the strong winds often blow sand over the roads.
• Many places are accessible only by camel, which is a traditional form of transport in the region.
• Public transport often involves seriously overladen buses. 

• Desertification - happens when land is gradually turned into a desert, usually on the edges of an existing desert.
• This can occur when land is overgrazed by livestock or stripped of vegetation by people collecting firewood. 
• Once exposed to the weather, it will crack and break up. It will then be eroded by wind and water. 

Where is desertification a problem?

• Most of the areas at risk from desertification are on the borders of existing deserts, e.g, the Sahara Desert in Africa. 

Causes of desertification:
Climate change -

• Rainfall - climate change is expected to reduce rainfall in areas that are already quite dry.
• Less rain means less water is available for plant growth, so plants die.
• Plant roots hold the soil together.
• If the plants die, the soil is easily eroded.

• Temperatures - global temperatures are expected to increase.
• Higher temperatures mean that water evaporates from the land and from plants.
• This makes soils drier and means that plants die.

Human activities - 

• Removal of fire wood - many people in arid areas rely on wood for cooking. Removal of trees leaves the soil exposed so it is more easily eroded.

• Overgrazing - too many cattle or sheep rat the plants faster than they can regrow.
• This leads to more soil erosion because the plants no longer hold the soil together.
• Trampling by animals also erode the soil.

• Over-cultivation - if crops are planted in the same area continually, all the nutrients in the soil get used up.
• This means that plants can no longer be grown in those soils and, without plants, soil erosion increases.

• Population growth - this puts pressure on the land, leading to more deforestation (for firewood) and more overgrazing and more over-cultivation. 

The loss of plants means that the soil is more easily eroded, making it less fertile and so less able to support plants. Management strategies aim to reverse this process.

Different strategies for reducing the risk of desertification:

1. Water management 

• Growing crops that don't need much water can reduce water use.
• Using drip irrigation on crops instead of surface irrigation means that the soil isn't eroded by lots of water being added all in one go.

2. Tree planting

• Trees can be planted to act as windbreaks to protect soil from wind erosion.
• Trees can also be used to stabilise the sand to prevent the desert from encroaching on farm land.
• Growing trees in amongst crops protects the crops and soil by providing shade, which reduces temperatures and evaporation rates. 

3. Soil Management 

• Leaving areas of land to rest in between grazing or planting lets them recover their nutrients.
• Rotating crops that use different nutrients from the soil means that the same nutrients don't keep being removed.
• Compost can be used to add extra nutrients to the soil.

4. Appropriate technology

• Involves using cheap, sustainable and extra available materials that are easy for local people to maintain.
• E.g, sand fences or terraces can be constructed to stabilise the soil and reduce erosion.
• The rate of deforestation can be reduced by using solar cookers, which use the sun's energy to heat food.
• They are cheap and easy to make, and don't require fuel wood to work.